Anticoagulant therapy is required to perform a number of clinical procedures including coronary artery bypass graft (CABG) surgery and other "open-heart" surgeries, percutaneous coronary interventions (PCI, "angioplasties"), and dialysis; and is also used as a treatment for a number of thrombotic diseases including acute coronary syndromes (heart attacks and unstable angina), deep vein thrombosis, pulmonary embolism, and peripheral vascular disease. The major toxicity and limitation of anticoagulant therapy is serious drug-induced bleeding. For example, transfusions due to blood loss are required in upwards of 50 percent of CABG surgeries and 10-15 percent of PCI procedures. Thus, there is a critical need for safer anticoagulants, particularly agents whose activity can be readily controlled, to reduce the number and magnitude of such bleeding events. Regado Biosciences, Inc. is addressing this unmet need by developing the first generation of regulatable (i.e., antidote-controlled) therapeutics. In Regado's Regulatable Drug Discovery Platform, the drug is comprised of a nucleic acid aptamer, and the antidote is comprised of an oligonucleotide that is complementary to a portion of the drug. The Company's primary focus is the discovery and development of antidote-controlled antithrombotics, and its lead drug discovery program is its Regulatable Anticoagulants Program. The Company is currently developing an antidote-controlled antagonist, REG1 and its matched antidote, REG1 AD, against coagulation factor IXa (FlXa) for use in open-heart surgeries and angioplasties. In 2000, there were more than 500,000 CABG surgeries and greater than 1,000,000 PCI procedures performed in the U.S., and FIXa is a validated target for anticoagulant development for these indications. The REG1 drug-antidote pair has been validated in the test tube and in patient plasma samples (Rusconi et al, Nature 419, p. 90-94, 2002), and more recently in a small-animal model of arterial thrombosis and in small and large animal models of anticoagulation and drug neutralization (see preliminary data). While the REG1 drug-antidote pair has performed well in these studies, REG1 has not been fully stabilized to prevent its degradation by bodily endonucleases, nor has it been fully minimized to enable more cost-effective manufacturing. Therefore, in its current form, REG1 may require higher doses to maintain a needed biologic effect over time and have higher manufacturing costs as compared to a fully optimized compound. Our Overall Goal is to fully optimize the REG1 drug-antidote pair to generate candidate compounds for preclinical and clinical testing. The Specific Aims of this proposal are 1) To optimize the coagulation FlXa inhibitor REG1, leading to the selection of a preclinical/clinical candidate anticoagulant and 2) To optimize the neutralization activity of the antidote for REG1, leading to the selection of a preclinical/clinical candidate REG1 antidote. Completion of the experiments proposed will position the Company to initiate IND-enabling non-clinical studies and ultimately human clinical studies with fully optimized candidate compounds.